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Under low normal stress condition, the pore among the fine gravel grain is too small to be filled by the fine grain during the process of direct shear.
Then, the interlocking action among the fine sand grain is broken by the shear stress, and the grain tumbles back and forth, which makes the volume expand.
Grain Breakage of Fine Gravel.
The volume of the fine gravel contacts obviously because the pore among the gravel grain is filled with the tiny grain under high normal stress condition.
The figure indicates that the number of the tiny grain increases after the grain breakage, which makes the fine gravel from bad gradation to good gradation.

In fully recrystallized samples, grain size measurements were done by using line intercept method (ASTME112) to obtain grain growth versus annealing time relation at different temperatures and plotted in Fig. 1.b.
Nucleation observed (a) along the grain boundaries and (b) inside the twins (white circles).
The presence of more complex deformation mechanisms in swaging, which probably generated higher stored energy and larger numbers of preferred nucleation sites, is believed to be the reason of differently sized grains obtained after the same heat treatment.
Preferred nucleation sites were observed to be the twinned regions and grain boundaries.
Grain growth kinetics of bulk AZ31 magnesium alloy by hot pressing. 

The surface grains are gradually uniform, and the grain size is 2.1mm.
Most of them are still distributed in the grain, and the particles attached to grain boundaries and sub-grain boundaries also begin to increase.
Under the same process, the number of precipitates of 2# steel significantly reduces, and they are uniformly distributed in the crystal.
The higher the recrystallization rate is, the faster the volume number of precipitates grows
(2) The number of Cu2S and MnS in the precipitates is similar at the end of deformation.

Each of the mc-Si blocks is wire-sawed into a number of mc-Si wafers of certain thickness such as 200um.
Grain boundary.
Heterogeneous nucleation can be formed near the crucible wall result in generating fine grain and producing a large number of grain boundaries at the same time.
Heat stress direct result in the grain produced a large number of dislocations [10-11].
Grain distribution was not uniform in the wafer, the grain size on the side adjacent to the crucible was smaller, and the grain size on the other side is relatively larger.

The grain refinement can improve its ductility and formability.
The objective of the present work is to establish randomisation of texture to increase work hardening exponent by favourably orienting a large number of grains (texture) in AZ31 alloy to improve its stretch formability by promoting additional straining in thickness direction. 1.
Many techniques namely ECAP, HPT, and ARB can be used for grain refinement of bulk metallic alloys.
Microstructural observations indicated that decrease in grain size is favourable for increase in percentage of elongation while increase in grain size after deformation due to dynamic recovery favours improvement in stretch formability.
New deformation mechanism in fine grain Mg alloys.

The grain size was decreased with carbon content due to grain boundary pinning.
Equiaxied grains were formed regardless of carbon content.
On the other hand, in the C-added alloys, TiC particles existed inside of grains and at grain boundaries.
Although the linearity in Fig.7 is not good and the number of data is a few, σ0 and k are evaluated to be 165 MPa and 1322 MPa µm1/2, respectively.
The grain size reduction must be due to grain boundary pinning by TiC

The different conditions of finishing stage of TMCP adopted here are described as follows, respectively with respect to start strip thickness and number of passes applied during finishing stage: - #0: no formal holding stage; - #1: 30 mm; one pass; - #2: 30 mm; two passes; - #3: 50 mm; three passes.
The comparison of these micrographs suggests that grain size of the #0 is the finest.
It can be seen that the contribution of grain size is predominant.
As expected, higher holding thicknesses and number of passes during finishing rolling increased total rolling time and decreased the productivity of the Steckel Mill Line.
Gladman, Grain-Refined C-Mn Steels, Journal of the Iron and Steel Institute, February 1967, 161-182

In a micro metal forming process, it is possible that only a small number of grains are directly involved.
Experiments Grain Size.
Grains clearly deformed near the inner surface of the cups.
Fig. 8 shows the load increased as grain size decreased.
Fig. 8 Effects of punch speed and grain size on load References [1] M.

The properties of welded joint will been improved by these fine crystal grain.
Following the increasing of magnetic field current, the number of α-Mg increases and displaies as equiaxed grain, the β-Al12Mg17 is diffusion distribution at the grain boundary of α-Mg.
The grain consists of coarse α-Mg and series β-Al12Mg17.
Large surplus of aluminum accumulate along the grain boundary at this time, which make the Aluminum rich in grain boundary and segregate the α-Mg.
The crystal grain will be coarsening and the properties of welded joint will deteriorate.

By contrast, in the work of Xia et al. [11] the nanostructured martensite in Cu-Al alloys obtained by high-pressure torsion (HPT) decomposed to an ultrafine-grained duplex equiaxed grain structure more quickly than in conventional martensite with large lath widths.
The present investigation was conducted to examine the evolution of the structure and the phase composition of the Cu-Al alloy subjected to HPT under different numbers of rotations.
Figure 1(a) shows the as-received sample with an average grain size of ~1 mm.
For the HPT-processed samples, the microhardness becomes higher because HPT leads to a refinement of the grains [12, 14].
It means also that decomposition of the nanostructured martensite includes inhomogeneous nucleation and grain growth.